In this work is reported the bending sensing characteristics of a long-period grating produced point-by-point with a
266 nm Nd:YAG laser. Spectral changes of the transducer subjected to bends with curvatures from 0 to 3.13 m-1 were
investigated. The magnitude of the bend-induced wavelength shift is nonlinear and dependent on the rotation of the
cylindrical fibre relative to the bending plane. For each constant bending applied to the grating, the fibre was rotated
around its axis in angular steps of 15º, within the angular range from 0 to 180º. An artificial neural network model was
applied for identifying the curvatures, resulting in a root-mean-square error of 0.028 m-1.
This work shows the use of long period gratings in the petroleum sector, in two specific applications. The proposed
sensors are employed both to identify substances in a simulated flow inside a pipeline, and to assess the gasoline
conformity commercialized in gas stations. The gratings responses for each specific case were employed to train and to
validate two different topologies of artificial neural networks: perceptron multilayer and radial base function. The
obtained results show that fiber optic sensors supervised by artificial neural networks can constitute systems for smart
measurement with high applicability in the petrochemical field.
We report an alternative technique to interrogate a long-period fiber grating (LPG) when the grating sensitivity is based on the peak amplitude changes of the resonant wavelength. To read the amplitude changes, a conventional optical domain reflectometer was used. Bend measurements were performed to apply such method and to determine the grating sensitivity for this physical parameter. Reflective measurements, temperature insensitive, and the possibility of multiplexing LPG sensors are some advantages offered by this technique.
A compact sensor able to discriminate between temperature and strain related effects was implemented. The proposed sensing head comprises a single long-period grating with two sections written consecutively in the SMF-28 fiber, by the electric arc discharge technique, using different fabrication parameters. The sensor performance is based on the distinct temperature and strain sensitivity values presented by two neighbor resonances belonging to each grating section. The temperature and strain resolutions are ± 0.1 °C and ± 40 με, respectively.
This work shows the use of a long period grating to analyze the quality of a commercial gasoline blend. Samples with different single and double solvent proportions are characterized. It is shown that the addition of controlled amounts of a standard solvent allows differentiating legal blends from tampered blends. With the proper choice of that solvent, it is possible to shift the LPG operation towards a higher sensitivity range, and even samples that deviate little from the legal gasoline blend can be identified.
We report the rocking filter formation in a circular, a bow tie and in an elliptical core optical fiber by the technique of internal light exposure. The visible Argon ion laser lines in 488.0 and 514.5 nm, with circular polarization, are used as the writing beam source, and the obtained filters shown coupling efficiency between 2.5 and 60 percent. For similar exposure parameters, elliptical core fiber lead to higher efficiency couplers as compared to the stress induced birefringent fibers.
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